GATE has now become important as some 4/5 PSUs are recruiting through it. It should require preparation for about 3/4 months to crack this exam. From 2013, GATE was made online. So, one has to be thoeugh with the concepts.Yes ! CONCEPTS hold the key as the questions are generally easy but conceptual.
The 15 marks of english and mental ability should not require any special preparation as such. In fact, this area is quite scoring.
questions from The 15 mark section(not sure of the weightage) of engineering mathematics are usually very easy. But due to the length/coverage of the syllabus, people tend to go unprepared. DONT DO this mistake. I found GATE maths book by made easy very suitable for this regard.
Regarding chemical engineering courses all of them are important and must be throughly prepared. I shall soon come up with the detailed strategy and books I followed for this section. good bye for now!